how to differentiate multi channel Rx and Tx

[masary]

Hello,
I'm new in CCS. I have one Receiver and one transmitter which have 6 channels and working at same frequency. I'm using ccp1/2 to measure the pulse width. I only got 2 pulse width. With this condition, I only can built 2 tasks. I want to built each channel to do different task. Do you have any ideas how to do that?
Thanks

[SherpaDoug]

What are you transmitting or receiving? is it RF or IR or something else? How are these "channels" supposed to be differentiated? How is the data encoded on the signal? We really don't have enough information to start.
_________________
The search for better is endless. Instead simply find very good and get the job done.

[masary]

sorry..it is RF.
Actually the these Tx and Rx come from helicopter remote control. All channels working at the same freq, around 45hz. The pulse length (for every channel) is related to stick position, e.g: all the way to the left 1 ms, middle 1.5 ms and all the way to the right 2 ms.

How are these "channels" supposed to be differentiated?

I want my PIC can differentiate each channels. I dont have any idea besides measure the pulse lenght but this only have 2 conditions.


How is the data encoded on the signal?
actaully i dont really understand this. I got lil bit info. -->receiver does not have much signal processing to do - just to divide the pulses to each of it's servo outputs and watch out for the synchronization pulse to reset the channel counter

[rberek]

I'm still not entirely clear on what you are trying to do.

Are you trying to receive 6 PWM channels and transmit 6PWM channels simultaneously, or are you just trying to receive 6 simultaneously?

Either way, I don't see how that is possible with a single PIC. If you are processing 6 input channels simultaneously you need to capture data for all the channels at the same time, since input will be occurring all the time on every channel (I have 3 RC helicopters. Believe me, none of the sticks ever stops moving for very long).

With one PIC, you cannot process six channels at the same time. If you have a multiplexer in front of the PIC to select two of the six input channels, you will be able to process two data streams, but you will miss the data being transmitted on the other four channels during that time. And that is only if you are processing receive channels. If you are also trying to transmit data, you will have to split your processing time among twelve operations with two CCP modules. As well, if you intend on transmitting the PWM servo signals, which are nominally 500 Hz or so, you may find you have to run the PIC at a low clock frequency, which reduces your processing power.

Its late and maybe I'm not getting your point. Can you describe in more detail what you are trying to do?

r.b.

[Mark]

[rberek]

Interesting. Shows how much I know!

[masary]

mark--> yes, the RC receiver never send the pulse at the same time. but i dont know how to make PIC recognize it. I use cpp1 and cpp2 to measure pulse width.

so, how to built/make PIC can detect pulse at different time by using port b? what kind of interrupt that you mention?

thanks..

[Mark]

If you don't want to add external IC's then do as I have said. The portb change interrupt will give you 4 channels. You will need to let a timer run. Anytime an interrupt fires, check to see if one of the outputs has changed. If so, then if it is high grab the timer value. If it just went low, then take the current timer value and subtract the previous timer value (the one when the timer went high). You will of course need to check for the timer roll over and handle it. The other 2 channels can be measured with the external interrupt or with the CCP module. If there is enough separation between the channels, you can OR them together and feed them to an external interrupt. Feed this signal into the CCP input as well. On the external interrupt, reset the timer and start the CCP to capture on falling edge. Also look at each channel to see which one is high. Set a variable (index) to represent this channel. On the CCP interrupt, store the CCP value into an array where the element is the index from the external interrupt. This will allow you to measure each pulse. You should make sure that the CCP interrupt has the higher priority since you will most likely be getting the external interrupt and CCP interrupt very close together. Since the pulse widths are relatively long (>1ms), if the 2 interrupts occurring about the same time give you too much trouble, then you could do an edge detect and delay the output and feed this into the external interrupt. Since the delay time is fixed, you would just adjust for it in the results.

[SherpaDoug]

I have never used RC servos but I have heard that the signal is sent like this:
There is a burst of pulses sent at some regular interval. The width of the first pulse is for the first servo channel where 1ms is one extreem and 2ms is the other extreem. The width of the second pulse controls the second channel. Each successive pulse is for another channel. The gap between bursts reselects the first channel.

So the receiver detects the RF signal and demultiplexes the channels by just counting leading edges, and resetting when there is a gap. That should be an easy job for a PIC. The PIC doesn't need to time how wide the individual pulses are, just count the leading edges and time out when pulses stop comming.
_________________
The search for better is endless. Instead simply find very good and get the job done.

[Mark]

[Humberto]

SherpaDoug,
I�m agree with the exact and concise explanation of a today's normal operation of multi-channels R/C servos, except in the following paragraph:

[Mark]

[Humberto]

Mark wrote:

[Mark]

[Humberto]

Mark wrote: